This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-371891, filed on Dec. 6, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus that has a fixing device for fixing a developer image formed on a recording medium. A high frequency magnetic field is generated from a coil and given to a heating member to generate eddy-current, and a developer image on the recording medium is fixed through the self-heating of the heating member based on the eddy-current loss.
2. Description of the Related Art
In an image forming apparatus utilizing the digital technology; that is, a so-called digital copier, a fixing device equipped with a heating roller and a pressing roller which are in contact with each other is practically used for fixing a developer image on a sheet of paper by the heat of the heating roller while conveying a sheet of paper by clamping it between these rollers.
As an example of the heat source of the heating roller, there is an induction heating device. This induction heating device is provided with a coil accommodated in the heating roller and a high frequency generator for supplying high frequency current to this coil.
The high frequency generator is equipped with a rectifier circuit for rectifying AC voltage and a switching circuit for converting the output voltage (DC voltage) of this rectifier circuit into a prescribed high frequency. The above-mentioned coil is connected to the output terminal (the output terminal of the switching circuit) of this high frequency generator.
When the high frequency generator is operated, high frequency current is supplied to the coil and a high frequency magnetic field is generated from the coil. This high frequency magnetic field is given to the heating roller and eddy-current is generated in the heating roller. Then, the heating roller is self heated by this eddy-current loss and a developer image on a sheet of paper is fixed by this heat generation.
In the such a fixing device, a warming-up process to raise a temperature of the heating roller to a prescribed temperature when the power is turned ON and a pre-run process to make the surface temperature of the heating roller uniform by rotating the heating roller after the warming-up process is executed.
In such a fixing device, a method is proposed to judge errors according to a time lapse up to temperature arriving points at plural stages in the warming-up process when the power is turned ON.
The errors referred to here are such defects expected that a prescribed temperature is not reached within a prescribed time, a circuit board for executing the induction heating is damaged or wires are pulled out or defects of a temperature detector and thermistors, etc.
The above-mentioned digital copier is so constructed that an ADF (Automatic Document Feeder), a finisher, a FAX function, a printer function, an ADU (Auto-Duplex Unit) function can be set as options.
Further, it is proposed that the electric power to be applied to the coil is variable based on the set state of the options in the warming-up process when the power is turned ON.
So, such a copier that is capable of varying electric power to be applied to a coil according to the setting state of options in the warming-up process and a subsequent pre-run process when the power is turned ON, and setting a comparative time (an error detecting time) up to temperature arriving times at plural stages when executing the warming-up process to raise a temperature of the heating roller to a prescribed temperature when the power is turned ON is demanded.
The present invention is made in view of the above demand and its object is to provide an image forming apparatus that is capable of varying electric power to be applied to a coil based on the option setting state in a warming-up process when the power source is turned ON and a subsequent pre-run process, and setting error detecting times up to temperature arriving times at plural stages when executing the warming-up process to raise a temperature of the coil to a prescribed temperature when the power source is turned ON and the subsequent pre-run process based on the electric power applied to the coil.
According to the present invention, an image forming apparatus is provided. This image forming apparatus is capable of setting various options, has a coil in a heating roller, generates eddy-current in the heating roller by generating a high frequency magnetic field from the coil and has a fixing device to fix a developer image on a recording medium by the self heating of the heating roller based on the eddy-current loss. This image forming apparatus comprises: first judging means for judging a comparison time until the temperature reaching points at plural stages when executing the process to raise the temperature of the heating roller to a prescribed temperature when a power source is turned ON; processing means for executing the process to raise the temperature of the heating roller to a prescribed temperature by applying a prescribed electric power to the coil when the power source is turned ON; detecting means for detecting the temperature of the heating roller along the lapse of time in the processing by the processing means; and second judging means for judging whether there is any error according to a time elapsed to arrive at temperature points at plural stages judged according to detected temperature by the detecting means and a corresponding comparative time that is judged by the first judging means.
Further, according to the present invention, a method is provided for detecting errors when supplying electric power to the heating device in the image forming apparatus that is capable of setting various options and has a fixing device that has a coil in the heating roller, generates eddy-current in the heating roller by producing a high frequency magnetic field in the coil and fixes a developer image on a recording medium through the self-heating of the heating roller. This error detecting method comprises: judging a comparative time to the temperature reaching points at plural stages when executing the process to raise the temperature of the heating roller to a prescribed temperature when the power source is turned ON based on the set options; executing the process to raise the temperature of the heating roller to a prescribed temperature by applying a prescribed electric power to the coil when the power source is turned ON; detecting the temperature of the heating roller along the lapse of time when executing the process; and judging whether there is any error according to a time elapsed to the temperature arriving points at plural stages judged according to the detected temperature and a corresponding comparative time that is judged by the first judging means.